Are kilts considered proper meeting or assembly attire in the UK?

Yes, I have been to Perth (that's the one in Scotland, not Oz) Convention and there are always a few brothers here and there wearing tartan kilts. I have also known them to be worn at weddings. I haven't heard anyone say "He is wearing the garb of a woman, stone the blasphemer!!!" at any convention - well not yet anyway!

I've never seen any kilts being worn at JW conventions or meetings in Canada. However, I have seen traditional garments from other countries. I was told the "rule of thumb" was that it had to be consistent with the person's land of origin, otherwise you were expected to conform to local custom and dress according to what was considered to be appropriate business attire.

Yes, you always get a couple of attention seekers at Perth Convention wearing them, but most commonly they're worn at weddings. Some don't think they're appropriate for the platform and I have never seen one being worn a speaker. I recall some English halls being a bit circumspect of them even being worn for weddings.

But they must be tartan. I have one in dark grey tweed and some Witnesses went bananas just hearing about it.